The present invention relates to a method and a device for detection of impact loosening of thread joints at rock drilling.
When drilling long holes in a ground, for example rock, several rods are used which are screwed together in order to lengthen the drill string as needed during the drilling. The tightening of the threads normally becomes so firm as a consequence of the shock waves passing the thread joints during drilling, that the thread joints cannot be loosened only with the assistance of the rotation motor of the rock drilling machine. In order to solve this problem, the operator ends the drilling by letting the impact device exert the drill string to impacts for a short while without pressing the drill string against the ground. The operator stops the impact device when a characteristic change of sound is heard. After that, the drill string can be unscrewed with the rotation motor of the rock drilling machine, and the separate drill rods can be picked up one by one. A drawback of this method is that one cannot automate the taking up of the drill string when automatic drilling has occurred. Another drawback is that the operator has difficulties in hearing that the impact loosening has occurred at an early stage because of the noisy environment. This gives rise to unnecessary wear on the drilling equipment.